Regression-test `table(scheduled(at = col_name))` syntax

From our macro code:

let scheduled_at_column = scheduled_at_column.ok_or_else(|| {
    syn::Error::new(
        sched.span,
        "scheduled tables must have a `scheduled_at: spacetimedb::ScheduleAt` column. \
                 if the column has a name besides `scheduled_at`, you can specify it with \
                 `scheduled(my_reducer, at = custom_scheduled_at)`",
    )
})?;

This syntax, with the at = col_name parameter supplied, does not appear in our docs, and is not regression-tested.

Definition of Done

Add a use of this syntax to the module-test module so that it gets built in CI

Locate the module-test module and inspect how scheduled tables and reducers are currently declared. Add a case using table(scheduled(at = col_name)), then build the module or run the relevant CI test to confirm the syntax is accepted and remains covered.